[ 



THE BLOOD. 685 



importance, a brief resume of their characteristics, based on the descriptions of EhrUch and of 

 Da Costa, ^ may appropriately here find place. 



It should be noted that the differentiation of these cells is founded upon not only their 

 morphological characters, but also the behavior of the granules embedded within their cyto- 

 plasm when subjected to certain combination stains. A generation ago Ehrlich divided the 

 aniline dyes into three groups— arid, basic, and neutral. The first includes such dyes as acid 

 fuchsin, orange G or eosin, in which the coloring principle acts or exists as an acid and exhibits 

 an especial affinity for the cytoplasm. The second group, the basic stains, includes dyes, as 

 hematoxylin, methylene-blue, methyl-violet, methyl-green or thionin, in which the coloring prin- 

 ciple exists chemically as a base in combination with a colorless acid and particularly affects the 

 chromatin ; hence, such are nuclear stains. Neutral dyes, produced by mixture of solutions of 

 an acid and a basic stain, have a selective affinity for certain so-called neutrophilic granules. 



Assuming that the blood-film has been fixed by heat and tinged with Ehrlich's "triacid 

 stain" (a combination of solutions of acid fuchsin, orange G, and methyl-green) the following 

 varieties of colorless cells are distinguishable in normal blood : 



1. Small Lymphocytes. — These are non-granular cells, with an average diameter of .0075 

 mm. or about that of the erythrocytes, distinguished by a large deeply staining nucleus that 

 occupies almost the entire cell. The meagre cytoplasm is reduced to a narrow peripheral zone, 

 so inconspicuous that it may be overlooked. The small lymphocytes, which constitute from 

 20-30 per cent, of all the white corpuscles, are the most common derivative from the lymphoid 

 tissues. 



2. Large Lymphocytes, or Mononuclear Leucocytes. — These elements, about .012 mm. in 

 diameter, possess a relatively small round or oval nucleus, which is usually eccentrically placed 

 and so poor in chromatin that it stains faintly. The cytoplasm is non-granular and comparatively 

 large in amount. 



3. Transitional Leucocytes. -Assuming that the lymphocytes and leucocytes are related 

 and not distinct elements, the transitional forms represent the developmental stage linking the 

 large lymphocytes with the mature leucocytes. Their distinguishing feature is the indented or 

 kidney-shaped nucleus which usually occupies an eccentric position within the- non-granular 

 cytoplasm. The latter, as well as the diameter of the transitional forms, corresponds with that 

 of the large mononuclear leucocyte. 



4. Polymorphonuclear Leucocytes. — These represent by far the most common type of 

 white cells, of which they constitute about 70 per cent. Their diameter is approximately .oic 

 mm., hence they are somewhat smaller than the transitional forms, but larger than the red cells. 

 Their cytoplasm is relatively large in amount and contains fine neutrophilic granules. On 

 account of the great diversity of the forms that they assume, the nuclei are very conspicuous 

 features of this type of leucocyte. At first sight the nuclei appear multiple; closer examination, 

 however, shows the seemingly distinct nuclei to be connected by delicate processes, so that, 

 although exceptionally two or more isolated nuclei exist and the cells are truly polynuclear, 

 their actual condition is appropriately designated as polymorphonuclear. 



5. Eosinophiles. — Leucocytes of this type are conspicuously distinguished by the coarse, 

 highly refractive granules within the cytoplasm that display an especial affinity for acid dyes, 

 particularly for eosin. These resemble the polymorphonuclear leucocytes in size (.010 mm.) 

 and in the character of their nuclei, the latter, however, in general being less distorted and 

 commonly eccentrically placed. The eosinophiles are prone to rupture, after which the pale 

 nucleus lies in the midst of a swarm of brightly tinged granules. 



Although other types of colorless cells, as myelocytes and mast cells, are of clinical interest, 

 they do not occur in normal blood and, hence, need not be here discussed. An occasional addi- 

 tional type of leucocyte, the basophile cells, is rarely present in normal blood. These elements 

 resemble the polymorphonuclear leucocytes, but are distinguished from the latter by the presence 

 within the cytoplasm of closely packed fine granules that possess a strong affinity for basic dyes. 



In the foregoing grouping the varieties of white cells are regardeid as different stages of 

 elements genetically related and derived from the same sources — a view supported by the early 

 development of the leucocytes. It should be mentioned, however, that Ehrlich and many other 

 hematologists consider the lymphocytes and the leucocytes as entirely distinct elements, believing 

 the former to be derived from lymphoid tissues and the leucocytes exclusively from bone-marrow. 

 Accordingly, the large lymphocytes and the large mononuclear leucocytes are of different nature, 

 although, as universally admitted, their assumed differentiation is at best uncertain. The presence 

 of all forms of white cells in the circulation of the embryo long before the appearance of bone- 

 marrow ( Ebner) seems conclusive evidence that the origin of tfie leucocytes is not limited to the 

 marrow tissue. 



The Blood Plaques. — In addition to the erythrocytes and leucocytes, the 

 blood of man and other mammals reg^ularly contains small bodies, the blood plaques 



^Clinical Hematology. Phila., 1901. 



